As well known, there are various methods for producing a carbon nanotube, such as an arc discharge method, a laser vapor deposition method and a chemical vapor deposition method (CVD method).
The arc discharge method is a method wherein graphite is enabled to vaporized through the generation of arc discharge between a positive graphite electrode and a negative graphite electrode, thereby creating a deposition of condensed carbon on a distal end of the negative electrode and forming carbon nanotube in the deposition of condensed carbon (see for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-95509). The laser vapor deposition method is a method wherein a graphite specimen mixed with a metallic catalyst is placed in an inert gas atmosphere which is over-heated to high temperatures and then subjected to laser irradiation, thereby forming carbon nanotube (see for example, Jpn. Pat. Appln. KOKAI Publication No. 10-273308).
Generally speaking, although it is possible in the cases of the arc discharge method and the laser vapor deposition method to create carbon nanotube having an excellent crystallinity, the quantity of carbon nanotube created is small, thus it is considered difficult to create carbon nanotube in large quantities.
The DVD method can be classified into two methods, i.e. a substrate method wherein carbon nanotubes are formed on a substrate placed in a reaction furnace (see for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-86217) and a fluidized gas phase method wherein a carbon source is fluidized together with a catalytic metal in a high-temperature furnace, thereby creating carbon nanotube (see for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-342840).
The vapor phase deposition method will be explained with reference to FIG. 6. The reference number 1 in FIG. 6 represents a reaction tube in which a catalyst-carrying substrate 3 having a catalyst 2 carried therein is positioned. Electric heaters 4 are disposed on an outer circumference of the reaction tube 1. A raw material (hydrocarbon) 5 is allowed to flow into the interior of the reaction tube 1 from one side of the reaction tube 1 and to discharge from the other side of the reaction tube 1. As a result, a hydrocarbon gas 6 is generated in the interior of the reaction tube 1, thereby forming carbon nanotube. Incidentally, the reference number 8 in FIG. 6 represents a hydrocarbon gas.
Next, the fluidized gas phase method will be explained with reference to FIG. 7. In FIG. 7, the same components as those of FIG. 6 are identified by the same reference numbers, thereby omitting the explanation thereof. The system shown in FIG. 7 is characterized in that a hydrocarbon 5 employed as a raw material is fed together with a carrier gas 8 from one side of a reaction tube 1. By doing so, a hydrocarbon gas 6 is enabled to generate at an inner region of the reaction tube 1 which corresponds to the region where an electric heater 4 is disposed, thereby making it possible to form carbon nanotube 7.
However, since the aforementioned vapor phase deposition method is performed by way of a batch treatment, it is difficult to utilize for mass production. Further, in the case of the fluidized gas phase method, it is poor in uniformity of temperature and hence considered difficult to create carbon nanotubes exhibiting excellent crystallinity. On the other hand, there is proposed an innovated type of fluidized gas phase method, wherein a fluidizing material also acting as a catalyst is employed for creating a fluidized layer in a high temperature furnace, and a carbonaceous raw material is fed to the furnace to create fibrous carbon nanotubes. However, in the case of this method also, it is poor in uniformity of temperature and hence considered difficult to create carbon nanotubes exhibiting excellent crystallinity.
Therefore, if it becomes possible to effectively and cheaply mass-produce fibrous carbon nanotubes which are highly useful such as high-purity/high stability carbon nanotubes, high-purity/high stability carbon fibers, high-purity/high stability carbon nanocoils, etc., it may become possible to supply nano-technology products utilizing the characteristics of carbon nanotube in large quantities and at a low cost.